Photo-electric tube



Patented July 26, 1932 UNITED STATES PATENT OFFICE ARCHIE J. MCMASTER AN'D CHARLES PABSON, OF CHICAGO, ILLINOIS, ASSIGNORS TO- G-M LABORATORIES, INC OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS rHoro-nLEcrRIc mu Application filed June-14, 1930. Serial No. 461,119.

Our invention relates to a photoelectric tube and a method of making the same.

In photoelectric tube a plate of large area is provided which is processed and treated .to form a light. sensitive electron emissive surface thereon. The final sensitivity of the tube depends upon factors which must be.

as the description proceeds.

Referring to the drawing: Fig. 1 is a side elevation of a photo-electric tube embodying our invention and made in accordance with the method of our invention, and v Fig. 2 is a similar view of the tube rotated through an angle of 90 degrees.

The tube comprises a base 6 on which an envelope 7 is mounted, and within the envelope is a stem or press 8 upon which the elements of the tube are mounted. A pair of laterally extending supports '9 and His mounted on thestem and carries a plate 13 which constitutes the cathode of the tube. Forwardly of supports 9 and 11 is a support 12 which serves as the anode of the tube. At the upper end of the cathode a support 14 is secured thereto which mechanically connects the cathode with the anode by means of an insulating connecting member 15, pref erably of glass or some other refractory material. This mechanical connection between the upper ends of the anode and cathode tends to hold them in fixed spaced relation,

and prevents the production of microphonic" noises due to relativev vibration between the anode and cathode. A disc 19 supporting a pellet 21 is secured to the upper end of the 'anode. Thispellet consists of a salt of alkali or alkaline earthmetal, mixed with calcium or some other element having a higher affinity for the element or radical of the salt than the alkali or alkaline earth metal. Upon inductively heating the disc and pellet the calcium replaces the alkali or alkaline earth metal of the salt and liber ates metallic alkali or alkaline earth metal.

The cathode 13 consists of a conducting metal such as copper, gold, silver, magnesium, or the like, or it may consist of a copper plate having a coating of silver or gold, electroplated or otherwise deposited thereon as described in our co-pending application,

Serial No. 461,117 filed June 14, I930. The

cathode has a coating of barium oxide, strontium oxide, potassium dichromate, or a mixture oftwo or more of these compounds ap plied thereto. The process of applying this coating is partially conducted prior to mount ing the cathode in the envelope, and is comlo pletedin the envelope. The method of coating the cathode with any of the above compounds may be identical. If the coating is to consist of barium oxide for example, barium carbonate is mixed with a solution of '15 nitro-cellulose in methyl alcohol and amyl acetate, and is thoroughly milled in a'ball mill to insure an intimate mixture of the ingredients. This. mixture is then sprayed upon the cathode, in which process the sol-- vent is substantially evaporated so that the barium carbonate and nitro-cellulose binder reach the cathode in substantially dry form, forming a coating of sufiicient hardness to permit handling'of the cathode.

After the cathode. and other elements have been mounted in the envelope as shown inthe drawing, the cathode is inductively heated to burn the nitro-cellulose and convert the barium carbonate to barium'oxide by the liberation of carbon dioxide. During this process the envelope is exhausted to carry away the gases produced by the conversion alkaline earth metal from the pelletand de- 100 osit it uponthe cathode. The envelope is eated in an oven during this time to prevent the metal from collecting on the inner walls thereof. After the metal has been deposited'upon the cathode the process of heatmg and evacuating. the tube is continued.

The heating at this point has two functions. It causes the formation of an alkali metal oxide which absorbs some of the alkali metal, and a thin adsorbed layer or film of the alkali metal is formed overlying the mutually absorbed alkali metal oxide and alkali metal. The second function of the heating is to ex-' pel any excess of alkali metal from the bulb in cooperation with the evacuation of the The process has been described in connection with a coating of barium oxide on the cathode. However, the process for coating the cathode with other oxides such as those enumerated 'above' is identical.-

Anotlier method of coatin the cathode which is also applicable to arium oxide, strontium oxide, potassium: dichromate, silver oxide, or a mixture of two or more of these oxides, is to mix the oxide with an aqueous solution of barium nitrate. This mixture is applied to the cathode and al-- lowed to dry. The cathode is then,mounted in the envelope as shown in the drawing and the cathode is inductively heated. The cathode is then coated with a thin film of an alkali metal as described above.

The particular type of alkali or alkaline earth metal deposited upon the oxide coating depends upon the final characteristics desired in the tube. If it is desired to produce a'tube having a maximum response to long wave lengths such as those in the region of yellow and red of the light spectrum, acasium salt is used in the pellet such as caesium chloride, caesium carbonate, caesium nitrate, or the like. If a tube having its maximum use for shorter wave lengths is desired, an alkali salt such as potassium chloride, potassium carbonate, potassium nitrate or the like is used in the pellet. If a tube having its maximum respouse to still shorter wave lengths is desired,

an alkaline earth metal salt such as barium, strontium, or magnesium carbonate may be used in the pellet It will be understood that-the nature and embodiments of .the invention herein described and disclosed are merely illustrative and that many changes and modifications may be made therein without departing from the spirit and scope of the invention.

What we claim as new and desire to protect 1 by Letters Patent of the United States is:

1. A method of producing a light sensitive surface on the cathode of a photoelectric tube which consists of forming a solution of an "oxygen compound, applying the solution to the cathode, applying heat to. evaporate the solvent, and allowing an oxide-to remain on metal oxide applied thereto, and

the cathode, and depositing an alkali metal upon said oxide.

2. A method of producing a light sensitive surface on the cathode of a photoelectric tube which consists of forming an alkaline earth metal oxide on the cathode, and depositing an alkali metal on said oxide.

3. A method of producing a light sensitive surface on the cathode of a photoelectric tube which consists of applying a metallic oxide to the cathode, and depositing a light sensitive electron emissive metal upon said oxide.

4. A method of producing alight sensitive surface on the cathode of a photoelectric tube e, mounting the cathode the cathode, and depositing a film of alkali metal on jthe oxide, and removing the excess of said metal from the cathode.

6. A photoelectric tube comprising an envelope, an anode and a cathode mounted therein, said cathode having an alkaline earth a'film of alkali metal over said oxide.

7. Aphotoelectric tube comprising an envelope, an anode and a cathode mounted.

therein, said cathode having an alkaline earth metal oxide applied thereto, and a film of caesium over said oxide. 8. A photoelectric tube comprising an envelope, an anode and a cathode mounted therein, a layer of barium and strontium oxides on said cathode, and a film of alkali metal over said layer.

In witness whereof, we hereunto subscribe our names this 6th day of 'June, 1930.

ARCHIE J. MCMASTER. CHARLES E. PARSON. 

